One of the critical parameters in the operation of a gaseous discharge device such as a display panel is the operating margin of the device which is defined as the range between the maximum sustain voltage V.sub.S max. and the minimum sustain voltage V.sub.S min. However, the fabrication process for gas panels is relatively complex and variable whereby the operating voltages required for individual panels may vary quite substantially, such that it is essential to determine and regulate the amplitude of the sustain signal on a panel-by-panel basis. Even by selecting a voltage level at some point within the normal operating range of the panel, the margin of the panel would be severely restricted if the panel was operating toward either end of the operating range rather than at an intermediate point therein. It is therefore essential that a means be provided for obtaining the appropriate sustain level on a panel basis to utilize the full operating margin for each panel. Additionally, provision must be made to compensate for variation in sustain signal levels resulting from aging, temperature variation or other operational characteristic variations.